Wind-thermal environment in idealized 2D street canyon with different aspect ratios and thermal conditions

Environmental problems such as low wind speed, poor air quality and urban heat island effect are deteriorating in cities due to the rapid urbanization. Optimizing the ventilation condition in the urban canopy is an effective way to improve the urban air quality and thermal environment. To study the impact of building structure and thermal condition on local flow regime and micro thermal environment, wind tunnel experiments and CFD simulations were conducted with scale-model of idealized 2D street canyons. A series of street canyon models with aspect ratios of 1.1, 2.4, 4 and 5.67 were set up for both wind tunnel experiments and CFD simulations, with the scaled ration of 1:200. Laser Doppler Anemometer was deployed in the working section of the wind tunnel to monitor the velocity components. CFD simulations using ANSYS Fluent 15.0 were performed to study the turbulence characteristics under wind driven force and thermal buoyancy force. A solar ray tracing model and radiation models in Fluent was employed to simulate the heat effect of solar radiation in street canyons. The wind tunnel experiments and modelling revealed that a clockwise vortex existed in regular and deep street canyon while two counter-rotating vortexes appeared in extremely deep canyon. Moreover, different turbulence structures and significant spatial variation of air temperature existed in canyons with different solar elevation.